If there is one book CNH Tours recommends you read before going to the Galapagos it's SONG OF THE DODO, ISLAND BIOGEOGRAPHY IN AN AGE OF EXTINCTIONS by David Quammen.

This is not a novel, nor a book particularly focused on Galapagos (though the islands do feature in the book, and the author has traveled there to meet some of the locals).   But it's a book that, in a fascinating and often very entertaining read, will give you a strong foundation for better understanding why Galapagos is such a special place.   It's part travel log, part popular science and by using many colourful examples, tells the story of how islands are a powerful force behind biological evolution.  Also, perhaps one of the most poignant lines in the book, Quammen explains why "islands are where species go to die".

The book was perhaps one of our best appreciated wedding gifts (we were married 3 weeks before moving to Galapagos).  My husband read it three times while we where there!